Leadframes are used in most integrated circuit packages. Most kinds of integrated circuit packages are made by placing a silicon chip on a leadframe, then wire bonding the chip to the metal leads of the leadframe, and then covering the bonded structure with plastic, usually an epoxy-based thermoset compound. A leadframe is essentially a thin layer of metal that connects the wiring from tiny electrical terminals on the semiconductor chip surface to the large-scale circuitry on electrical devices and circuit boards. Most leadframes are typically produced on a single, thin sheet of metal by stamping or etching to allow them to be quickly processed on the assembly line.
Prior to incorporating the leadframe in the integrated circuit package, a surface of the leadframe may be subject to various processes including plating and/or roughening to enhance adhesion between the leadframe and the epoxy during the packaging process. For example, the leadframe surface may be roughened by treating the leadframe with a chemical etchant. Further, the leadframe surface may be plated with a noble metal or metal alloy. These processes may be designed with the goal of reducing the tendency of the leadframe and plastic epoxy to separate as a result of differing thermal-expansion rates between the metal of the leadframe and the plastic of the package following prolonged exposure to moisture.
Although roughening and plating the leadframe surface may enhance adhesion properties of the leadframe, it may also affect the color and reflectivity (brightness or glossiness) of the leadframe surface. Further, due to process variations like current density, chemical concentration, equipment standards and the like during the leadframe plating and roughening processes, it may be difficult to precisely control the color and reflectivity of the surface of the leadframes from one batch to the next, thereby creating color and brightness inconsistencies of the leadframe surface. Still further, such color and brightness (reflection) variations may be difficult to quantify and standardize.
Consistency of the color and brightness of the leadframe surface may be important in a package production line that heavily relies on pattern recognition. More specifically, in the package production line, machines for performing a variety of processes including dispensing epoxy on top of the leadframe surface, die bonding, wire bonding, mount process, molding treatment, strip test process and the like may rely on pattern recognition. For example, in the mount process on the package production line, a machine may perform pattern recognition based on color and brightness of the leadframe surface to determine epoxy volume or epoxy shape dispensed on a leadframe surface. Even if there is a slight variation in the color and/or brightness of the leadframe surface, the machine may not accurately distinguish the leadframe surface from the epoxy and as a result, the pattern recognition process may fail or be performed incorrectly, thereby resulting in a significant loss of productivity and increase in cost on the assembly line.